Electric spark plug



Oct. 29, 1935. l.. GRAF ELECTRIC SPARK PLUG Filed April 22, 1933 Zim/en far.'

ea rf 2'/ Ww Patented 29, 1935 ELECTRIC PATENT OFFICE SPARK PLUG Leo Graf, Cologne, Germany Applicatim April 22, n

6 Claims.

The present invention relates to an electric spark plug which meets the requirements of every kind o1' internal combustion engine, independently of the degree of compression and the speed. I 'I'he plug is thus adapted for universal use. It is common knowledge that internal combustion engines are run at various degrees of compression and speed and that, in order to comply with the needs of service, almost alike number of dillerent kinds oi' sparkplugs are in existence. The "plug provided by the invention is designed for use on every class of internal combustion engine.

The plug is so constructed that both the iiring point and the cooling are increased to the extreme limit so that, on the one hand,` it is a matter oi' impossibility for the plug to glow with'following self-ignitions in high-compression engines, and, on the other hand, it is possible to forego the self-cleaning temperature to avoid sooting-up and oiling, even in a case of engines running under low compression and at a low speed, said drawback being eliminated by other means, namely, by providing ample means of protection against sooting-up of the insulator and the nring electrode. The conventional plugs used for fuel mixtures with a high degree of compression in high-speed engines have a firing point which is considerably lower than the temperature required for self-cleaning where the plugs have to operate in low-speed engines designed for low-'compression fuel mixtures, with the result that they are useless for these engines. On the other hand, the plugs in use for low-speed engines are useless for high-speed engines working on high-compression mixtures, on account of selI-ignitions. In the design embodied in the invention the earth electrode itself seals the joint so that the cooling effect is obtained with the greatest rapidity, with the iurther result that the possibility is given of maintaining a high tiring temperature. The new device may be used for producing either a single spark or several sparks, thus providing the means of igniting the heaviest mixtures, or of operating with the following spark gap in case ot shortcircuiting of one spark gap, until the short-circuited spark gap is free again.

The construction embodied in the invention is shown in the accompanying drawing by way oi example, in which- Fig. l is a sectional elevation of the spark plug,

Fig. 2 is an elevation or the insulating core,

Fig. 3 is an elevation of the plug.

Fig. 4 is a partial section showing a double air gap,

Figs. 5 and 6 are cross-sections on the lines HoIFlg.2and-lofFlg. 3.

The current for the spark plug passes through the tiring stem b fitted in the insulating core a 1933, Serial N0. 667,459

Germany January, 1933 to the metallic cap c forming one of the electrodes of the plug, while the other, the earth electrode, is formed by the metallic sleeve d which is drawn a comparatively long distance over the insulating core a, preferably of conical shape with the smaller diameter at the bottom, and fitted, similarly to the seat of a valve, as an extended cone gas-tight in corresponding conical bores e, f of the plug body g serving as an earth electrode. The electrodes d and c are separated by an air gap formed as an annular slit h. In the insulating core a beneath the air gap h the annular groove i is located as a protection against sooting-up. This annular grlve, which communicates with ,fthe sparking gap, forms a separate space for the gas mixture in which the latter is red, the explosion wave being driven through the slits h into the cylinder where combustion of the gas mixture and that contained in the cylinder takes place, with the re- 20 suit that the explosion in the annular groove i constantly cleans the annular slit h of soot. The cap electrode c lies sunk within the threaded portion k of the plug body, an open annular space l being formed between the cap c and the threaded member k. This annular space communicates with the annular slit h, representing the spark gap, which is thus disposed in a protected position in the neighborhood of its base and protected from t-he deposit of soot. The annular sleeve d makes a tight joint with the insulator and serves as an earth electrode, ai-r channels formed by annular chambers m, n being provided which communicate with the outside air for the circulation of cooling air through the medium of apertures o, p serving for cooling ol! the earth electrode. The cooling effect of the current-conducting cap electrode c is further promoted by the metallic member q of the lower end of the metallic stem of the insulating body, 40 this member having the shape of a comparatively thick rivet head, its location being made possible by transferring the spark gap from the lower face of the insulating core to the sleeve d at the point h. n

The insulating core is secured in the plug bodyv by a nut r through the interposition of .the elastic, copper-asbestos ring s and in the sealed pressedposition of its corneal sleeve d in the conical bores e, f.

As shown in Fig. 4, the spark gap is increased nearly two-fold by the insertion of a metallic washer in the annular slit h, serving as an air gap, between the cap c and the conical electrode d, this metallic washer separating the inner space containing the gas-mixture, which is formed by the annular groove i, into two annular spaces u. v and at the same time the air gap into two annular slits.

I claiml. A spark plug for internal combustion engines having a core of insulating material inserted in a plug body, a metallic stem insaid core for conducting the firing current. a long conical metallic sleeve, acting as an earth electrode, drawn over this core and iltted gas-tight in a corresponding conical bore of the plug body, and a cap on the insulating core in circuit with said metallic stem, said sleeve and cap being separated by an air gap for producing the firing sparks kon the insulating core.

2. A spark plug for internal combustion engines having a core of insulating material inserted in a plug body, a metallic stem in said core for conducting the tiring current, a long metallic sleeve, acting as an earth electrode and fitted lgas-tight in a corresponding conical bore in the plug body, the plug body being interrupted by an annular groove and provided with apertures which are led outwardly from said annular chamber for the circulation of cooling air round the earth electrode, and a cap on the insulating core in circuit with the metallic stem, said sleeve and cap being separated by an air gap for producing the iiring sparks on the insulating core.

3. A spark plug for internal combustion engines having a core oi insulating material inserted in a plug body, a metallic stem in said core for conducting the ring current, a long metallic conical sleeve, acting as an earth electrode, drawn over this core and fitted gas-tight in a corresponding conical bore of the plug body, the bore being interrupted by a plurality of annular grooves with apertures Ain the plug body which are led outwardly from said annular chamber for the circulation oi cooling air round the earth electrode, and a cap on the insulating core in circuit with said metallic stem, said sleeve and cap being` separated by an air gap for producing the firing sparks on the insulating core.

4. A spark plug for internal combustion engines having a core of insulating material inserted in a plug body, a metallic stem in said core for conducting theilring current, a long metallic sleeve, acting as an earth electrode. drawn over this core and fitted gas-tight as a current conductor in a corresponding bore of the plug body, and a cap on the insulating core in circuit with said metallic stem, the sleeve and cap being separated by an air gap for producing the firing 5 sparks on the insulating core, and an annular groove in the insulating coreat said air gap between the sleeve and cap acting as an insulator and provided for protecting the electrode from sooting-up.

5. A spark plug for internal combustion engines having a core of .insulating material inserted in a plug body, a metallic stern in said core for conducting the ring current and having a cap thereon, a long metallic conical sleeve acting as a grounded electrode relative to the plug body. said sleeve providing a gas-tight connection between the plug body and the core acting as a current conductor in a corresponding conical bore in circuit with said metallic stem, the sleeve and cap being separated by an air gap for producing tiring sparks on the insulating core, and an annular enlargement onv the insulating core above the conical sleeve, a yieldable pressure ring on the upper annular shoulder of the Vannular enlargement, and a nut adapted to t the thread on the outer end of the plug body, the nut pressing the insulating body with its conical sleeve, acting as an earth electrode, on to the conical surfaces of the bore of the plug body to ensure perfect gas-tightness.

6. A spark plug for internal combustion engines comprising a plug body, a core of insulating material in said body, a metallic stem in said core, a long metallic sleeve around the core and between it and the body, and a cap on the inner end of the core in contact with the stem and sur-* rounding the end of the core but spaced from the,4A`- long metallic sleeve, the insulating core adja-f' cent the space between the sleeve and the cap o having a groove therein forming an explosion chamber for the gases ignited by the sparks formed between the sleeve and cap.

LEO GRAF. 

